Ethylene copolymers make up a large segment of polyolefin polymers and are representative of the class. Such polymers range from crystalline polyethylene copolymers to largely amorphous elastomers, with a new area of semi-crystalline "plastomers." In particular, ethylene-.alpha.-olefin and ethylene-.alpha.-olefin-diolefin elastomers are a well established class of industrial polymers having a variety of uses associated with their elastomeric properties, their thermo-oxidative stability, their solubility in hydrocarbon oleaginous fluids, and their ability to modify the properties of polyolefins. Included in this elastomer terminology are both EPM (ethylene-propylene copolymers) and EPDM (ethylene-propylene-diolefin terpolymers) rubber, both being vulcanizable by cross-linking, the addition of the diolefin providing increased ease of both cross-linking and functionalization. The vulcanized compounds are used in traditional thermoplastic applications when used with fillers, particularly in the automotive industry for such as belts, hoses and seals, in rubbery blends such as tire sidewall applications where they can be co-vulcanized with other rubbers, as roof coating materials, and in thermoplastic elastomeric alloys wherein the EPDM is dynamically vulcanized in a matrix of other thermoplastic polymer so as to create a dispersed phase of vulcanized elastomer in plastic. The rubbery characteristics of EPM and EPDM can provide toughening properties to any of a number of polar monomer based engineering thermoplastics, particularly when functionalized. Further the EPM and EPDM can both serve as effective viscosity modifiers for fuels and lubricating oils and can additionally provide dispersant and oxidative stabilizing characteristics for those oleaginous compounds when functionalized with polar functionalities including those based on amine and carboxylic acid moieties. Uses of the plastomers include general thermoplastic olefins, films, wire and cable coatings, polymer modification (by inclusion in blends with other polyolefins), injection molding, foams, footwear, sheeting, functionalized polymers (such as by free-radical graft addition of polar monomers) and components in adhesive and sealant compounds.
With the advent of metallocene catalysts, certain processes have become available for both EPM and EPDM. A bulk, or slurry, process utilizing supported, biscyclopentadienyl Group 4 metallocenes activated with alumoxane co-catalysts is bridged described as suitable for EPM and EPDM in U.S. Pat. No. 5,229,478. It is stated therein that prior art metallocene/alumoxane catalyst systems, directed to the preparation of ethylene-.alpha.-olefin elastomers, typically produce low molecular weight polymer not suited for use as a commercial elastomer. Thus advantages of higher molecular weight and high diene conversion rates are emphasized. The patented process utilizes metallocene compounds having alkyl, silanylene or silaalkylene bridged cyclopentadienyl ligands in a slurry of supported catalyst in liquid .alpha.-olefin. This process illustrates the use of support techniques and materials adding to the complexity and cost of the method for industrial use.
Catalysts comprised of metallocene cations and noncoordinating anions found to be suitable for the polymerization of ethylene copolymers are described in U.S. Pat. No. 5,198,401. Extensive description of noncoordinating anions is presented and Examples 29 through 33 address ethylene copolymer elastomers having varying molecular weights (M.sub.n from 21,000 to 317,000) and high .alpha.-olefin content (e.g., about 25 mol. % and about 65 wt %) using a catalyst based on bis(cyclopentadienyl) hafnium dimethyl at polymerization reaction temperatures of 50.degree. C. In the related publication EP 0 277 004 hafnocenes activated with anion providing catalyst components are said to be preferred for high molecular weight products and for increased incorporation of olefins and diolefin comonomers with ethylene. Each describes a preferred noncoordinating anion tetra(pentaflourophenyl) boron, [B(pfp).sub.4 ].sup.- or [B(C.sub.6 F.sub.5).sub.4 ].sup.-, wherein the perfluorinated phenyl ligands on the boron makes the counterion labile and stable to potential adverse reactions with the metal cation complexes. Other aryl radicals are said to be suitable in addition to the phenyl radicals, napthyl and anthracyl are listed. U.S. Pat. No. 5,296,433 teaches the utility of borane complexes comprising tris(pentafluorophenyl)borane and specific complexing compounds. These complexes are said to allow higher molecular weight polymers when used with metallocenes for olefin polymerizaton due to increased solubility of the complexes in monomer or monomer solutions. WO 97/29845 describes the preparation of the organo-Lewis acid perfluorobiphenylborane, and its use to prepare and stabilize active, olefin polymerization catalysts. These cocatalysts are described as being less coordinating than tris(perfluorophenyl)boron, B(C.sub.6 F.sub.5).sub.3, and thus capable of providing higher catalytic activities. Generic description of the suitable cocatalysts according to the application include those of the formula BR'R" where B is boron with R' and R" representing at least one and maybe more fluorinated biphenyls or other polycyclic groups, such as napthyl, anthryl or fluorenyl.
Processes for the preparation of syndiotactic polypropylene are addressed in U.S. Pat. Nos. 5,132,381 and 5,155,080. These patents address the use of asymmetric metallocenes for the sought stereospecificity. The latter addresses increased molecular weight and melting point syndiotactic polypropylene accessible with hafnocenes activated with methylalumoxane. Also, Ewen, et al, disclosed in J. Am. Chem. Soc., vol. 109, pp. 6544-6545 (1987) that rac-ethylene(bis(indenyl))hafnium dichloride provided higher molecular weight isotactic polypropylene than did the zirconium or titanium analogs.
High temperature processes for ethylene copolymers include those described in U.S. Pat. Nos. 5,408,017, WO 96/33227, WO 97/22635 and EP 0 612 768. Each describes metallocenes, including hafnocenes, that are said to be suitable for increasing molecular weight or catalyst activity, or both, used with noncoordinating anion cocatalyst components. High molecular weight ethylene/.alpha.-olefin copolymers is an objective of EP 0 612 768 and is addressed with catalyst systems based on bis(cyclopentadienyl/indenyl/fluorenyl) hafnocenes which are combined with an alkyl aluminum compound and an ionizing ionic compound providing a non-coordinating anion.
Improvement in catalyst activities so as to increase the yield of polymer for a given weight of catalyst compound, increasing molecular weight for high comonomer content ethylene copolymers, and maintaining both at temperatures generally in excess of room temperatures are recognized objectives for industrial processes.